The prior art includes a variety of apparatuses and methods for directional drilling of vertical or non-vertical boreholes in geological formations for recovery of oil and gas.
Directional drilling may be performed with steerable motor systems, in which a drill string includes a bent tubular section and an internal mud motor that rotates a drill bit. Operation of the system is alternated between a rotary mode and a sliding mode to change the trajectory of the borehole. During the rotary mode, a torque device such as a rotary table or a top drive rotates the entire drill sting (including the drill bit) to advance the borehole in a substantially straight path. During the sliding mode, the mud motor rotates only the drill bit to slide the drill string along a curved trajectory dictated by the bent tubular section of the drill string.
Directional drilling may be performed with “push the bit” rotary steerable systems (RSS), in which a drill string includes a straight rotatable tubular section with a plurality of actuable pads near the drill bit. As the tubular section rotates, the pads radially extend and retract from the tubular section so that they apply a controlled resultant radial force to the borehole wall, and thereby force the axis of drill string in a desired direction. However, such systems require a relatively complex valve mechanism to synchronously control the extension of the pads to achieve the desired effect.
Directional drilling may be performed with “point the bit” rotary steerable systems, in which a drill string includes a straight rotatable outer tubular section with an inner drill bit shaft that is adjustable in orientation with respect to the outer tubular section. However, such systems require a mechanism, such as a servomotor, to adjust the orientation of the inner drill bit shaft with respect to the outer tubular housing.
Directional drilling may be performed with systems in which pads or equivalent parts are actuated to engage the borehole wall to limit rotation of a bent tubular section while rotation of an internal drill string advances the drill bit. For example, U.S. Pat. No. 6,059,661 to Simpson discloses a directional drilling system in which pressurized hydraulic fluid actuates pistons that force grip pads radially outward from a stabilizer to anchor the stabilizer in the wellbore. In one embodiment, a hydraulic pump internal to the system pressurizes the hydraulic fluid from an internal reservoir to an internal gallery to extend the grip pads. A remotely controllable valve may control the flow of hydraulic fluid between the reservoir and gallery. United States Patent Application Publication No. 2001/0052428 to Larronde et al. discloses a downhole steering tool in which guide members move to engage the borehole to hold a steering housing against rotation while a drill string rotates a drill bit. The guide members are actuated by hydraulic passage leading to a hydraulic pump incorporated within the steering housing and driven by an electrical motor supplied with power from a MWD pump. United States Patent Application Publication No. 2016/0138381 to Logan et al. discloses an apparatus for directional drilling that allows an uphole section of a drill string to be rotated while maintaining a desired orientation of a bent section of the drill string with the use of pads that can be urged outwardly to engage walls of the wellbore, but does not disclose how the pads are actuated beyond indicating that they are hydraulically actuated.
There remains a need for improved apparatuses and methods for directional drilling that are reliable and avoid such complexities of the prior art.